This invention relates to rotary preset tuners, and more particularly to improvements of such tuners wherein a desired one of a plurality of memory slugs is selected by the rotating operation of a tuning member capable of being rotated in any direction and the reciprocating movement of a sliding member connected to variable condenser elements. The sliding member is resiliently abutted against the selected memory slug to provide the tuning operation.
Prior art rotary preset tuners have been constructed such that when a tuning member is rotated to provide a tuning operation, the memory slugs slide and move on a guide cam face of a sliding plate or a sliding member to provide resilient abutting against a subsequent memory slug. Due to such construction, undesirable force necessarily acts upon the sliding plate, resulting in either a stress or a strain on the sliding plate itself and a guide portion of the sliding plate. When such prior art tuners are installed in a vehicle such as an automobile, this stress or strain may be released by the external vibration of the vehicle. As a result, the sliding plate will be slightly displaced with respect to the memory slugs against which the sliding plate is resiliently abutted and thus a fluctuation of tuning frequency is generated. For example, a displacement of the sliding plate by 0.01 mm will cause a fluctuation of frequency. If the fluctuation of this frequency is 3 KHz or more, the tuner will no longer be useable.
Further, when the above described sliding movement of the memory slugs is repeated for long period of time, the resiliently abutted surfaces between the memory slugs and the sliding plate will wear out and the preset position of the memory slugs may change to cause a fluctuation of frequency.